1. Field
Embodiments described herein generally relate to methods and apparatus for simultaneous generation and separation processes. More specifically, embodiments include a membrane reactor for use in an apparatus for gas to gas or gas to liquid simultaneous generation and separation processes. Also described herein are embodiments describing methods for forming nanocatalysts which may be utilized in simultaneous generation and separation processes.
2. Description of the Related Art
Coal and natural gas resources are projected to provide greater than 40% of global energy demand over the next twenty plus years. In order to abate the global warming by reducing greenhouse gas emission in power plants, industries, transportation, etc., advanced technologies are being developed to enable clean, efficient and environmentally friendly use of these energy resources. As one of the advanced conversion technologies, coal gasification provides an efficient and flexible approach to utilize abundant energy resources with minimized pollution to the environment. During a coal gasification process, coal is heated and exposed to oxygen and steam, and the oxygen and water molecules oxidize the coal and produce a gaseous mixture of carbon dioxide, carbon monoxide, water vapor and hydrogen. The gaseous mixture then undergoes a water gas shift (WGS) reaction to produce hydrogen. Various membrane reactors are used to simultaneously generate and separate hydrogen.
One example of a membrane reactor is a compact catalytic membrane reactor (CCMR). A CCMR typically includes a membrane module that has a catalytic film. The catalytic film includes a porous layer having nano-sized catalysts deposited therein. As reactant gases pass through the catalytic film, hydrogen gas is generated. The catalytic film is also integrated with a membrane layer permeable to the hydrogen gas. As the hydrogen gas permeates through the membrane layer, the thermodynamics of the reaction are shifted toward hydrogen production. The hydrogen gas is produced and separated simultaneously in the CCMR. However, persisting issues with membranes or membrane modules for simultaneous hydrogen generation and separation include sulfur poisoning and low hydrogen flux.
Typically, the WGS reaction involves a high temperature shift (HTS) followed by a low temperature shift (LTS). Commercial HTS catalysts include a combination of iron (Fe) oxide materials and chromium (Cr) oxide materials. However, the catalytic activity of HTS catalysts can be substantially reduced in sulfur feed gas environments. Commercial LTS catalysts, such as copper-zinc (Cu—Zn) materials, are very sensitive to less than 0.1 ppm sulfur, resulting in almost 100% activity loss.
Pre-sulfided catalysts, such as cobalt-molybdenum-sulfide (CoMoS) materials and cobalt chromium oxide-sulfide (CoCr2O4S) materials, have little or no obvious activity loss in sulfur-laden conditions. However, common pre-sulfided catalysts demonstrate low activity and sulfur loss during the WGS reaction, and methane byproduct formation in sulfur-free conditions. Without the need for pre-treatment of sulfur in syngas for WGS, operational and capital costs can be significantly alleviated or reduced.
Therefore, improved methods and apparatus for simultaneous generation and separation processes are needed.